(1) Field of the Invention
This invention relates to a molded foam resin formed by injection molding of foaming agent-containing resin, a process for forming the same and a speaker diaphragm produced thereof.
(2) Description of the Related Art
In Japanese Patent Application Laid-Open No. H8-207074 and H8-340594, disclosed is a process for forming a molded foam resin by injection molding using foaming agent-containing resin and a speaker diaphragm made of the molded foam resin.
In the above patent applications, there is shown process, in which a foaming agent-containing resin is injected into a mold and then, the mold is opened after a lapse of a designated period of time after the completion of the injection, during said period of time a part of the resin in the vicinity of inner surface of the mold is cured while a part of the resin distant from the inner surface of the mold is not cured, thereby allowing non-cured portion of the resin to foam upon opening of the mold, and produced are a molded foam resin and speaker diaphragm having a three layer-structure consisting of a foamed layer inside and a non-foamed skin layer outside.
The three layer-structure gives lightweight and high stiffness characteristic to the molded foam resin and speaker diaphragm.
The molded foam resin and speaker diaphragm produced according to the above process look monotone of color on their surfaces.
Recently, there has been a demand for designing the molded foam resin and speaker diaphragm with different tone of color on their surfaces.
As one of the solutions to meet with the above demand, painting the molded foam resin and the speaker diaphragm with defferent colors seems to be feasible, however, the painting causes a problem of high cost.
It is therefore an object of the present invention to solve the above problem and to provide a molded foam resin, surface of which can be designed easily at low cost, a process for forming the molded foam resin, and a speaker diaphragm.
In order to accomplish the above object, a first aspect of the present invention is to provide a molded foam resin formed by injection molding of foaming agent-containing resin, comprising a foamed zone having a three layer-structure consisting of a foamed layer inside and a non-foamed layer outside and a non-foamed zone having a single layer-structure consisting of a non-foamed layer.
A second aspect of the present invention is to provide the molded foam resin according to the first aspect of the present invention, in which thickness of the non-foamed zone is 0.5 mm or less.
A third aspect of the present invention is to provide a speaker diaphragm made of molded foam resin formed by injection molding of foaming agent-containing resin, comprising a foamed zone having a three layer-structure consisting of a foamed layer inside and a non-foamed layer outside and a non-foamed zone having a single layer-structure consisting of a non-foamed layer.
A fourth aspect of the present invention is to provide the speaker diaphragm made of molded foam resin according to the third aspect of the present invention, wherein thickness of the non-foamed zone is 0.5 mm or less.
A fifth aspect of the present invention is to provide the speaker diaphragm made of molded foam resin according to the third or fourth aspect of the present invention, wherein the speaker diaphragm is formed into a circular shape and the foamed zone is formed in such a dimension that is symmetrical with respect to a center of the speaker diaphragm.
A sixth aspect of the present invention is to provide a process for forming a molded foam resin containing foamed and non-foamed zones therein comprising the steps of injecting a foaming agent-containing resin into a mold and opening the mold after a lapse of a designated period of time after the completion of the injection, in which a cavity of the mold contains a thick space corresponding to the foamed zone and a thin space corresponding to the non-foamed zone, and the designated period of time is chosen so that a curing of the resin filled into the thin space is completed and a curing of the resin filled into the thick space is not completed.
A seventh aspect of the present invention is to provide a process for producing a molded foam resin containing foamed and non-foamed zones therein, comprising the steps of injecting a foaming agent-containing resin into a mold and opening the mold after a lapse of a designated period of time after the completion of the injection, in which a cavity of the mold contains a thick space corresponding to the foamed zone and a thin space corresponding to the non-foamed zone, and the designated period of time is chosen so that a curing of the resin filled into the thin space is completed and a curing of the resin filled into the thick space is not completed.
A eighth aspect of the present invention is to provide a process for producing a speaker diaphragm made of molded foam resin containing foamed and non-foamed zones therein, comprising the steps of injecting a foaming agent-containing resin into a mold and opening the mold after a lapse of a designated period of time after the completion of the injection, in which a cavity of the mold contains a thick space corresponding to the foamed zone and a thin space corresponding to the non-foamed zone, and the designated period of time is chosen so that a curing of the resin filled into the thin space is completed and a curing of the resin filled into the thick space is not completed.
A ninth aspect of the present invention is to provide the process for producing a speaker diaphragm made of molded foam resin according to the eighth aspect of the present invention, in which a tightening force applied to the mold is decreased after a lapse of the designated period of time.
A tenth aspect of the present invention is to provide the process for producing a speaker diaphragm made of molded foam resin according to the eighth or ninth aspect of the present invention, in which the foamed zone has a three layer-structure consisting of a foamed layer inside and a non-foamed layer outside and the non-foamed zone has a single layer-structure consisting of a non-foamed layer.
Thus, according to the present invention, provided are a molded foam resin and a speaker diaphragm that can be thinned, designed with different tone of color on surfaces thereof and lightened without deteriorating stiffness thereof, since they are produced in such a manner that they have a foamed zone having a three layer-structure consisting of a foamed layer inside and a non-foamed layer outside and a non-foamed zone having a single layer-structure consisting of a non-foamed layer.
In addition, the molded foam resin and the speaker diaphragm, structures of which are described above, can be easily obtained by the injection molding according to the present invention.